High-pressure threaded union with metal-to-metal seal, and metal ring gasket for same

Abstract

A metal ring gasket provides a high-pressure temperature tolerant metal-to-metal seal between subcomponents of a threaded union. The metal ring gasket is received in an annular cavity formed between mating surfaces of the subcomponents of the threaded union. The metal ring gasket is capable of maintaining a fluid seal even at very high temperatures resulting from direct exposure to fire. At high fluid pressures the metal ring gasket is energized because hoop stress induced by the fluid pressure forces the metal ring gasket into tighter contact with the subcomponents of the threaded union.

1. A threaded union comprising:
 a nut having a box thread that engages a pin thread formed externally on a first subcomponent of the threaded union and an upper annular shoulder that extends radially inwardly from a top of a main body of the nut, the upper annular shoulder abutting a flange that extends radially outwardly from an adapter collar that sits on an annular shoulder of a second subcomponent of the threaded union; 
 a mating end of the first subcomponent comprising a first annular groove that mates with a complementary second annular groove in a mating end of the second subcomponent, the complementary first and second annular grooves respectively having a sloped annular outer face that is convergent to a respective planar bottom surface of the respective annular grooves; and 
 a metal ring gasket received in the respective annular grooves, the metal ring gasket having a planar top face, a planar bottom face that is parallel to the planar top face, a cylindrical outer face that is perpendicular to the top and bottom faces, and an annular converging sloped surface between each of the planar top face, the planar bottom face and the cylindrical outer face, the metal ring gasket being elastically deformed, without any plastic deformation, by contact between only the respective sloped annular outer faces and the respective annular converging sloped surfaces when the first and second subcomponents are drawn together by the nut. 
 
     
     
       2. The threaded union as claimed in  claim 1  wherein the annular converging sloped surfaces are elastically displaced by about  0 . 003 ″ when the mating ends are drawn together by the nut. 
     
     
       3. The threaded union as claimed in  claim 2  further comprising a gap between all other surfaces of the metal ring gasket except the respective sloped annular outer faces and all other surfaces of the respective annular grooves except the respective annular converging sloped surfaces, after the mating ends of the first and second subcomponents are drawn together by the nut. 
     
     
       4. The threaded union as claimed in  claim 1  wherein the nut comprises a single piece construction. 
     
     
       5. The threaded union as claimed in  claim 4  wherein the adapter collar is a multi-piece construction that has an inner diameter dimensioned to encircle an outer surface of the second subcomponent and rest on the annular shoulder adjacent the mating end of the second subcomponent. 
     
     
       6. The threaded union as claimed in  claim 5  wherein the adapter collar further comprises an annular groove dimensioned to receive an inner edge of a segmented retainer secured to a top of the nut. 
     
     
       7. The threaded union as claimed in  claim 6  wherein the segmented retainer is secured to the top of the nut by threaded fasteners that are received in tapped bores in a top of the nut. 
     
     
       8. A threaded union that provides a metal-to-metal fluid-tight seal between mating ends of first and second subcomponents of a fluid conduit, the threaded union comprising:
 an annular groove in the respective mating ends of the first and second subcomponents, the respective annular grooves having a sloped annular outer face that is convergent to a planar annular bottom surface of the respective annular grooves; and 
 a metal ring gasket received in the respective annular grooves, the metal ring gasket comprising a planar top face, a planar bottom face that is parallel to the planar top face, a cylindrical outer face that is perpendicular to the respective top and bottom faces, and an annular converging sloped surface between each of the planar top and bottom faces and the cylindrical outer face, the metal ring gasket being elastically, but not plastically, deformed by contact between the respective sloped annular outer faces of the annular groves and the respective annular converging sloped surfaces of the metal ring gasket, without the elastic deformation being inhibited by contact between any other surface the metal ring gasket and any other surface of the annular cavity when the first and second subcomponents are drawn together by a single nut. 
 
     
     
       9. The threaded union as claimed in  claim 8  wherein the metal ring gasket is elastically deformed by about  0 . 003 ″ when the first and second subcomponents are drawn together by the single nut. 
     
     
       10. The threaded union as claimed in  claim 9  wherein the metal ring gasket is octagonal in cross-section. 
     
     
       11. The threaded union as claimed in  claim 8  wherein the annular converging sloped surfaces are respectively inclined at an angle of about 23° with respect to the cylindrical outer face. 
     
     
       12. The threaded union as claimed in  claim 8  wherein the mating ends of the first and second subcomponents comprise a pin received in a socket, and the annular grooves are respectively located on and end of the pin and in a bottom of the socket. 
     
     
       13. A threaded union between first and second subcomponents of a fluid conduit that are interconnected by a nut, comprising:
 a first annular groove in a pin end of the first subcomponent, a complementary second annular groove in a socket end of the second subcomponent that receives the pin end of the first subcomponent, the first and second annular grooves respectively having sloped annular outer faces that are respectively convergent to a planar annular bottom surface of the respective annular grooves; and 
 a metal ring gasket received in the respective annular grooves, the metal ring gasket having a planar top face, a planar bottom face that is parallel to the planar top face, a cylindrical outer face that is perpendicular to the top and bottom faces, and an annular converging sloped surface between each of the planar top and bottom faces and the cylindrical outer face, the metal ring gasket being elastically deformed, without plastic deformation, by contact between only the annular converging sloped surfaces of the metal ring gasket and the respective first and second sloped annular outer faces of the respective first and second annular grooves when the first and second subcomponents are drawn together by the nut. 
 
     
     
       14. The threaded union as claimed in  claim 13  wherein the metal ring gasket is symmetrical and octagonal in cross-section. 
     
     
       15. The threaded union as claimed in  claim 13  wherein the metal ring gasket has a cylindrical inner face that is parallel with the cylindrical outer face and forms a right angle with the respective top and bottom faces. 
     
     
       16. The threaded union as claimed in  claim 13  wherein the metal ring gasket is hexagonal in cross-section. 
     
     
       17. The threaded union as claimed in  claim 13  wherein the respective annular converging sloped surfaces of the metal ring gasket are respectively inclined at an angle of about 23° with respect to the cylindrical outer face. 
     
     
       18. The threaded union as claimed in  claim 13  wherein the single nut comprises an upper annular shoulder that extends radially inwardly and abuts a radial flange of an annular, multi-piece adapter collar having an inner diameter dimensioned to encircle an outer surface of the second subcomponent and to rest on an annular shoulder of the second subcomponent adjacent the mating end of the second subcomponent. 
     
     
       19. The threaded union as claimed in  claim 18  wherein the adapter collar further comprises an annular groove dimensioned to receive an inner edge of a segmented retainer. 
     
     
       20. The threaded union as claimed in  claim 19  wherein segments of the segmented retainer are secured to a top of the nut by threaded fasteners received in tapped bores in the nut.